The present disclosure relates generally to rivet setting, and more particularly to linear displacement sensing within a rivet setting machine.
Automated and robotically moved rivet setting machines are known. Exemplary machines for use with self-piercing rivets are disclosed in the following U.S. patents: U.S. Pat. No. 8,146,240 entitled “Riveting System and Process for Forming a Riveted Joint” which issued to Mauer et al. on Apr. 3, 2012; U.S. Pat. No. 7,559,133 entitled “Riveting System” which issued to Chitty et al. on Jul. 14, 2009; and U.S. Pat. No. 6,789,309 entitled “Self-Piercing Robotic Rivet Setting System” which issued to Kondo on Sep. 14, 2004. All of these patents are incorporated by reference herein. While these prior patents have been significant advances in the field, their automated control complexity is not always required for some more simple rivet setting situations. For example, these prior automated control systems are not always as fast as sometimes desired for each rivet setting cycle due to the many actions being sensed and compared, such as force sensing with a load cell, and electric motor current and/or voltage sensing.
Another conventional device is disclosed in U.S. Pat. No. 6,951,052 entitled “Fastener Insertion Apparatus and Method” which issued to Clew on Oct. 4, 2005, and is incorporated by reference herein. It is noteworthy that column 9, lines 20-25, of the Clew patent state that the “present method of maintaining the velocity of the cylinder part of the linear actuator so as to deliver a predetermined amount of energy to the rivet insertion process without relying on positional or force sensors eliminates those control problems.” Thus, Clew teaches away from use of a positional sensor and instead uses an angular velocity encoder which adds a different level of complexity since this is an indirect measurement based on electric motor control, including all of the component tolerance variations and component backlash gaps associated with its pulleys, belts, shafts, plunger and the like, thereby leading to inaccuracies.
In accordance with the present invention, a rivet setting machine is provided. In another aspect, a linear displacement sensor directly senses and detects a position of a rivet-setting punch relative to a nosepiece of a rivet setting machine. A further aspect provides a control system and software instructions for sensing the relative position of a punch and nosepiece used by a programmable controller to determine and monitor a rivet setting position without use of a force sensor, motor current/voltage sensor, or a rotation sensor. A method of operating a rivet setting machine is also provided.
The present rivet setting machine is advantageous over conventional devices. For example, in one aspect, the present machine, system and method allow for a much faster rivet setting cycle time due to the less complex sensed values and calculations required. Furthermore, the present machine, system and method are advantageously more accurate since a direct linear displacement measurement is employed. Another aspect advantageously mounts the linear displacement sensor adjacent to the nosepiece which improves the direct measurement and accuracy by avoiding multiple component tolerance and movement variations; this provides a direct punch position measurement relative to the nosepiece-clamped workpiece when determining and/or varying a rivet head-to-workpiece flushness condition. Additional advantages and features of the present invention will be apparent from the following description and appended claims taken in conjunction with the accompanying drawings.